Two way satellite communication systems may often include a forward (FWD) satellite link and a return (RTN) satellite link. These links may be utilized for transferring information (data) between a central station, for example a Gateway or a Hub, and one or more terminals, for example Very Small Aperture Terminals (VSATs). Such systems may utilize adaptive waveforms, like or similar to those defined in ETSI's DVB-S2 ACM (Digital Video Broadcasting-Satellite-Second Generation, Adaptive Coding and Modulation) and/or DVB-RCS (Digital Video Broadcasting-Return Channel via Satellite) standards, which may allow adaptive allocation of satellite resources on per terminal basis.
Adaptive techniques may often be used for mitigating the effects of satellite link fade, as may be experienced at terminals locations. In one such technique, feedback information regarding FWD link reception quality may be periodically transmitted by each terminal over the RTN link to a Hub, which may use the information for selecting modulation and FEC combinations (MODCODs) for transmission towards these terminals over the FWD link. Another technique often applied for counteracting fade may involve transmission power adaptation.
Practically all techniques used for mitigating the effects of satellite link fade include use of margins. However, a problem exists in higher frequency bands (for example the Ka-band), as conventional margins are inadequate. With changes in link conditions being more rapid and of higher magnitude, higher system margins compensate for such changes, which may occur in between estimations of the link conditions. On the other hand, system margins may be considered as overheads, i.e. they may reduce the total resources available for transferring information and/or result in requiring more expensive equipment (e.g. higher power transmitters, larger antennas, etc.). Hence a suitable solution is helpful to address these issues.
As previously described, ETSI's recommendations and standards may include disclosures of adaptive waveforms. The DVB-S2 recommendations (EN 302307) may disclose an Adaptive Coding and Modulation waveform for a FWD link. The DVB-RCS recommendations (EN 301790) may disclose a scheme for a return link supporting multiple channels of different symbol rates and multiple timeslot types with different modulation and coding properties. However, neither teaches how to determine appropriate parameters for each transmission, nor how to select system margins for countering changes in link conditions.
Methods for controlling transmission parameters, specifically transmission power, may be disclosed in U.S. Pat. No. 6,212,360 to Fleming et al (titled Methods and Apparatus for Controlling Earth-Station Transmitted Power in a VSAT Network). However, the methods that may be disclosed by Fleming are inapplicable to adaptive waveforms, as they do not account for possible changes in other signal parameters (for example symbol rate and MODCOD). Moreover, Fleming may have no teaching regarding the setting of system margins.
U.S. application Ser. No. 12/337,330 to Ben-Laish et al (titled Multi-Dimensional Adaptive Transmission Techniques), which is assigned to the applicant, discloses embodiments which can have quasi-error-free communication at a highest efficiency level available under changing link conditions and network configurations without requiring reservation of substantial power margins.
Furthermore, U.S. application Ser. No. 12/027,887 to Martin et al (titled Combined Open and Closed Loop Power Control in a Communications Satellite) may disclose a method for controlling transmission power at a terminal. However, Martin does not disclose anything regarding a system margin, nor it discloses use of said estimations for determining a system margin, either for optimizing throughput or for any other purpose.